The invention relates to a process for the fabrication of a biosensor.
Most chemical sensors based on cantilevers or microbeams use the well-known silicon technology.
These chemical sensors are functionalized with molecules which can have a specific interaction with the biological material.
The term then used is biosensors.
The uses of these highly sensitive sensors relate to the field of proteomics, of DNA or RNA strand hybridization and of cell culturing and screening.
The detection of the specific interaction is linked to the changes in weight or of force applied to a cantilever, or microbeam, also known as microlever.
This mechanical change is detected by a sensor external or internal to the cantilever. The silicon-based cantilevers, or microbeams, can be placed in series in the form of a matrix of sensors for improving the measurement statistics and also the signal-to-noise ratio, but also so as to have various specific chemical interactions at the same time. However, the schemes for external detection of the deflection of the silicon microbeam use mainly optical detection by reflection of a laser beam, which is known to those skilled in the art. This method is not very suitable for detecting deflection of a matrix of cantilevers because of difficulties in setting up one or more lasers and/or a lens for the serial or parallel reading of a whole matrix of microbeams. This will be all the more true if the matrix contains a very large number (more than about ten) microlevers operating simultaneously. Furthermore, poorly controlled air/liquid interfaces can generate measurement artifacts which prevent stable detection of the deflection of the microbeam in a biological solution.
Therefore, in order to remove these technical impediments of bulk detection of a matrix of sensors, internal detection such as with a piezoresistive, piezoelectric or magneto-impedance sensor has been used inside the microbeam.
Each embedded sensor is addressed by metal electrodes.
The detection of the mechanical change, when the biomolecule functionalizing the biosensor is brought into contact with the biomolecule or the analyte to be detected and/or quantified, can be carried out a) in dynamic mode when the cantilever is set to resonate at a frequency close to its resonant frequency in order to increase the sensitivity of the detection, or b) in static mode by detection of the deflection of the microbeam due to the modification of the surface stress of the microbeam during the capturing of the biomolecules.
Silicon technology is very expensive for using such internal sensors integrated into cantilevers of a few micrometers or even millimeters with electrodes. Furthermore, the electrodes conveying the electrical signal resulting from the internal sensor of the microlever are in direct contact with the biological solution in which the microlever operates. Given the highly conductive and ionic nature of the biological solution, and for obvious reasons of problems of short-circuiting and/or of corrosion of the metal of which the electrodes are composed, this device may not work in this case.